Oxygen Reduction Catalyzed by Au–TiO₂ Nanocomposites in Alkaline Media

Au-TiO2 nanocomposites were prepared by chemical deposition of gold nanoparticles onto TiO2 nanocolloids that were synthesized by a hydrothermal method. Transmission electron microscopic measurements showed that the TiO2 colloids exhibited an average diameter of about 5 nm and clearly defined lattice fringes that were consistent with those of anatase TiO2 and formed rather large agglomerates that spanned a few hundred nanometers in length. Additionally, gold nanoparticles were found to be embedded within the TiO2 matrices, and the size increased with increasing gold loading but all ranged from 10 to 50 nm in diameter. Consistent results were obtained in X-ray diffraction measurements. Electrochemical studies demonstrated that the resulting Au-TiO2 nanocomposites exhibited apparent electrocatalytic activity in oxygen reduction that was markedly improved as compared to that of TiO2 particles alone, as reflected in the onset potential, number of electron transfers involved, and kinetic current density. Among the series, the best catalyst for oxygen reduction was identified with the Au/Ti atomic ratio of 5.2%. The enhanced oxygen reduction kinetics was ascribed to the dissociation of water and formation of surface-adsorbed hydroxyl moieties that was facilitated by the loading of gold nanoparticles onto the TiO2 colloids.